Receptor Tyrosine Kinases

Question 1

What kind of molecule is EGF?

Answer 1

Polypeptide

Question 2

What evidence led to the theory that EGF binds to a receptor on surface and triggers multiple phosphorylations?

Answer 2

• When a cancer cell line was treated with EGF and radiolabelled ATP there was high phosphate incorporation into cells

Question 3

What does EGF do?

Answer 3

Triggers cell proliferation

Question 4

In absence of EGF what form are the receptors in?

Answer 4

Monomeric with inhibited kinase activity

Question 5

What happens to the EGF receptor when EGF binds?

Answer 5

• Dramatically alters the conformation and tethered region is free to interact with dimerisation arm on another receptor
• Transphosphorylation is enabled

Question 6

What are the advantages of EGF receptor heterodimerising?

Answer 6

• Provides flexibility and diversity
• Different combinations can bind different EGF-related ligands

Question 7

What does it mean for EGF receptors to heterodimerise?

Answer 7

They can bind to a different member of the EGF receptor family e.g. ErbB1 and ErbB3

Question 8

Why is ErbB2 the preferred dimerisation partner of other EGF receptors?

Answer 8

The dimerisation arm is always open

Question 9

Which EGF receptor is the preferred binding partner?

Answer 9

ErbB2

Question 10

What can ErbB2 not bind to?

Answer 10

EGF

Question 11

Why is the viral orthologue v-Erb constitutively active?

Answer 11

It has no outer cellular portion

Question 12

How does transphosphorylation of EGF receptor occur?

Answer 12

• When EGF binds the 2 kinase domains are brought together in close proximity
• One kinase domain phosphorylates the other and this activation allows the kinase to phosphorylate multiple tyrosine residues in the cytoplasmic tails of the receptor

Question 13

How can mutations in the kinase domain of the EGFr be oncogenic?

Answer 13

• Mutation in activation loop stabilises active conformation
• Kinase consitutively active and no longer relies on EGF signal

Question 14

Why is over-expression of ErbB2 oncogenic?

Answer 14

• Dimerisation arm always open and dimers are formed all the time
• Signal generated even in abscence of EGF

Question 15

How does the antibody herceptin clear ErbB2 and help to treat cancer?

Answer 15

• Size of antibody blocks it from coming close enough to another receptor
• Ligation by antibody leads to cleaving of the receptor from the cell surface

Question 16

What experiments are used to show proliferation by RTKs mechansims?

Answer 16

• Clone a gene into bacteria, each which a different one
• Lyse bacteria on filter and incubate with EGF phospho-tail and labelled ATP
• Radioactive signal if protein binds to receptor tail, identify and grow up bacteria and sequence

Question 17

How can different RTKs recruit different sets of molecules?

Answer 17

Have different cytoplasmic tails

Question 18

What does VEGF do?

Answer 18

• Stimulates chemotaxis and sprouting of capillaries
• Sensed by migratory cell tip

Question 19

Where do many non-RTKs couple to?

Answer 19

Cellular TKs

Question 20

Give an example of a non-RTK coupled to a cellular TK

Answer 20

• B cell receptor
• Essentially an antibody embedded in membrane and associates with dimer of proteins call CD78 and 79
• On activation of receptor, get activation of TKs